1. Field of the Invention
The present invention relates to medical devices for use in delivering a thrombolytic agent to a firm obstruction in a blood vessel and particularly to such a device having a configuration and system for effecting longitudinal extension through the firm obstruction as the obstruction is dissolved by the delivery of the thrombolytic agent.
2. Description of the Background Art
The acute symptoms of blockage of a vein at a venous valve or a partially sclerosed and narrowed artery may be instigated by the presence of a soft obstruction or blood clot that is soft and jelly-like in consistency. Such blood clots may form for a variety of reasons in the vascular system and be released and flow until they block a partially occluded section of the blood vessel. When this clot blocks a vessel in the leg, for example, the resultant pain or loss of circulation requires its removal or dissolution.
Such soft obstructions are readily penetrated but reform after the penetrating object is removed. To effect the initial opening of a soft obstruction, thrombolytic drugs or clot dissolving agents may be applied through an infusion catheter inserted into the clot to encourage the dissolution of the clot. For example, the infusion catheter disclosed in U.S. Pat. No. 5,085,635 is proposed to be introduced over a guidewire previously advanced through the soft obstruction and be used for infusion of thrombolytic drugs (as well as diagnostic agents, in other procedures) out side wall openings into contact with the soft obstruction.
Some obstructions or blood clots are not "soft" and are not subject to easy penetration by a guidewire or convertible wire and consequently are characterized as "firm" obstructions. The typical treatment is to gain access to one end of the firm obstruction and to infuse the thrombolytic agent in proximity to that end to dissolve it. In the use of conventional infusion guidewires, convertible wires or catheters for introducing the dissolving agent in such a fashion, it is not always possible to direct a concentration of the dissolving agent into the firm obstruction, where the infused agent would provide the most benefit. Some of the infused thrombolytic agent has the desired effect while the majority of the agent flows away from the site.
It would be desirable to provide local delivery of dissolving agents to a firm obstruction or firm blood clot to magnify the therapeutic effects while minimizing the complications, e.g. bleeding, of systemically delivered thrombolytic agents. Similarly, it would be desirable to apply and concentrate such agents into the firm obstruction as it shrinks in response to the treatment. Despite the advances and improvements in treatment that have been introduced in recent years, a need remains for an infusion guidewire and catheter that provides a simple and less expensive way to assure delivery of drugs or agents into a firm obstruction to achieve its rapid dissolution and restoration of blood flow through the blood vessel.
One way to speed the penetration and dissolution of the firm obstruction would be to apply firm pressure against the accessed end thereof as the agent is infused. However, despite efforts to make the tips of catheters and infusion guidewires soft, the application of force to penetrate a firm obstruction is problematic since any mistake in positioning of the tip may cause it to penetrate through the vessel wall or tunnel sub-intimal passageways alongside the vessel lumen and to pass by the firm obstruction without treating it.